Some indoor units of air conditioners are equipped with a casing with an opening provided at the front thereof and a movable panel. Such a movable panel is provided such that it covers the opening of the casing, and the movable panel opens the opening by moving away from the opening and closes the opening by moving close to the opening. In addition, in order to move the movable panel in such a way, indoor units of air conditioners are often equipped with a drive portion and a driving force transmission portion such as a gear and a cam for transmitting a driving force of the drive portion to the movable panel see, for example, Japanese Patent Publication No. 07-12821). By the driving force transmission portion, a driving force of the drive portion is transmitted to the movable panel, and the movable panel opens and closes.